1. Technical Field
The present invention relates to a membrane electrode assembly used for a power generation component of polymer electrolyte fuel cells (PEFCs) and a polymer electrolyte fuel cell using the membrane electrode assembly.
2. Related Art
Polymer electrolyte fuel cells using a proton conductive polymer membrane are being put into practice as a power source of mobile objects such as cars, since they can operate at a low temperature (ambient temperature) compared to the other fuel cells such as solid oxide fuel cells and molten carbonate fuel cells.
Such polymer electrolyte fuel cells (hereinafter also abbreviated as “PEFCs”) are typically configured such that a plurality of single cells each having a power generating function are stuck together.
Each single cell includes a membrane electrode assembly (MEA) that includes a proton-conductive polymer electrolyte membrane (e.g. NAFION (registered trademark) membrane), a pair of anode and cathode electrode layers (also referred to as “electrode catalyst layers”) that hold the polymer electrolyte membrane between them, and a pair of anode and cathode gas diffusion layers which hold the electrolyte membrane and the electrode layers between them. The gas diffusion layers (hereinafter also abbreviated as “GDLs”) are typically made of a carbon paper or a carbon cloth.
The membrane electrode assembly (hereinafter, also abbreviated as the “MEA”) of each single cell is electrically connected to the MEA of the adjacent single cell via a separator. The single cells are laminated and connected to each other in this way to form a fuel cell stack. Such fuel cell stacks are used for a variety of purposes as power generating means.
While various types of membrane electrode assemblies are known in the art, the above-described polymer electrolyte membranes fundamentally lack strength. To prevent breakage by a stress, which is caused by a pressure difference between fuel gas and oxidant gas, a thermal strain of the surrounding members and the like, and to prevent resultant gas mixing (cross leak), a variety of proposals have been made. For example, Patent Document 1 discloses a technique of coating the rim portion of electrodes and the outer rim of an electrolyte membrane with a reinforcing film made of fluororesin, polypropylene etc. in order to compensate for lack of strength at the outer rim of the polymer electrolyte membrane where the electrodes (gas diffusion electrodes) are not disposed.